A simple device for the conduct of stepped pressure filtration measurements is described together with methods for making the empirical measurements and interpreting the data obtained. The data interpretation method applies a multi-step systematic approach, with each step supported by statistical justification, to characterise: filter cake particle stress, filtration diffusivity and cake hydraulic resistivity from a single stepped pressure experiment. The methods enable different flocculant

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... rials to be more rapidly and more appropriately screened than conventional jar tests and large scale filtration trials. The methods are applied to the characterisation of a paint residue treated with aluminium sulphate and "PolyClay".<br>The work shows that the addition of "PolyClay" as a filter aide reduces the hydraulic resistivity at lower solids concentrations but increases it at higher concentrations whilst simultaneously increasing the particle stress. Together these have a combined deleterious effect on the time and energy required to dewater the residues to high solids concentration by filtration. The results also show that a significant change in suspension behaviour occurs between the "PolyClay" doses of 140 mg l^-1 and 660 mg l^-1 and that further changes up to "PolyClay" doses of 1600 mg l^-1 are more modest. The results indicate the existence an opportunity to reduce "PolyClay" dose into a range between 10% and 50% of current practice. In addition the results provide evidence that alternative, centrifuge based, technology is worthy of investigation.